Are there any circumstances where it is considered poor etiquette to
double? Example: I have 8 on my home board, opponent has six. I roll
double and now have 4, he rolls and now we each have 4 checkers on our
1 pts and its my roll. The only way I lose is if he rolls double
anything. I offered a double, he drops and calls me an #@$@$@.
My thinking is I want to win, right now if possible, why give him a
free shot at beating me when I can offer a double and take it down
right there. If he accepts, well god love him. Am I a jerk for doubling
there?

In OTB matches, it seems to me that this is an open insult -- you are
implying that you think your opponent is too stupid to see the gammon
chances.
On-line, there is an argument that people playing in a hurry (or for
turn based play, are trying to play too many games at the same time
and aren't paying attention), so there is some virtue in hoping for
such a mistake. I'd still consider it to be bad form. When an opponent
does this to me, the first time in a match I'll politely play on and
perhaps say something like I see enough gammon chances to make it
worth doing so. When it occurs again in the same match, I find it
insulting.
All in all, it's certainly rude and dubious sportsmanship.
In real life, it risks starting a major argument.